Theoretical models specifying the contribution of two social-familial mechanisms, negative reinforcement and affect dysregulation, to the development of child antisocial behavior were tested using a sample of 57 8- to 13-year-old boys referred for treatment of conduct problems. Negative reinforcement of boys' aggressive behavior and boys' affect dysregulation were found to covary with the boys' irritability toward parents and siblings and were reliable predictors of a composite measure of child antisocial behavior, defined by out-of-home placement, arrests, and school discipline incidents 2 years later. Reinforcement of aggression and affect dysregulation during family interaction may play complementary roles in the development of antisocial behavior by fostering the use of coercive means of dealing with social conflict. The findings are discussed in terms of research strategies for identifying social mechanisms contributing to child psychopathology and of implications for modification of current family interventions targeting child antisocial behavior.